The proposed work will deal with the identification of surface immunoglobulins on human lymphocytes by means of immunofluorescence with class-specific antisera. The lymphocytes of the peripheral blood will be studied in immunoproliferative disorders as well as in immunodeficiencies and in auto-immune diseases. A particular attention will be given to the Lg D class of immunoglobulins. Furthermore biochemical studies on the synthesis and turn-over of the surface immunoglobulins in the above mentioned conditions will be performed by radioactive labeling (either passively with I125 or actively by incubation with tritiated amino-acids) followed by analysis of the labeled surface of secreted proteins with class-specific antisera and polyacrylamide-gel electrophoresis.